The present disclosure relates to an audio signal processing apparatus, an audio signal processing method, and an audio signal processing program, which suppress noise.
A variety of techniques for suppressing a noise signal mixed in an audio signal have been proposed for the purpose of enhancing transmission quality and recognition accuracy of the audio signal. Examples of the conventional noise suppression techniques include the spectral subtraction (SS) method and the comb filter (comb-shaped filter) method.
However, in the spectral subtraction method, noise is suppressed only by noise information without using sound information, and accordingly, there have been problems of deterioration in the sound signal, and the occurrence of tone noise called musical noise. Moreover, in the comb filter method, there has been a problem that when an error occurs in a pitch frequency, then the sound signal is suppressed, or the noise signal is emphasized.
Japanese Unexamined Patent Application Publication No. 2006-126859 (Patent Literature 1) describes a sound processing apparatus that solves the problems of the spectral subtraction method and the comb filter method.
First, the sound processing apparatus described in Patent Literature 1 calculates a spectrum by frequency-dividing an input signal for each frame, and estimates a noise spectrum based on the spectra of a plurality of the frames. Then, based on the estimated noise spectrum and the spectrum of the input signal, the sound processing apparatus described in Patent Literature 1 identifies whether the input signal is a sound component or a noise component for each frequency division unit of the input signal.
Next, the sound processing apparatus described in Patent Literature 1 generates a coefficient for emphasizing a frequency division unit identified as a sound component and a coefficient for suppressing a frequency division unit identified as a noise component. Then, the sound processing apparatus described in Patent Literature 1 multiplies the input signal by the coefficient for each of these frequency division units, and obtains a noise suppression effect.